1. Field of the Invention
The present invention relates to an exhaust gas pipe assembly for an internal combustion engine mounted in an automotive vehicle.
2. Description of the Prior Art
An automotive engine is generally provided with an exhaust gas pipe assembly for discharging exhaust gases therethrough. In an automotive vehicle equipped with an internal combustion engine disposed longitudinally thereof, an exhaust gas pipe assembly includes a plurality of exhaust gas pipes extending rearwardly from the engine. The exhaust gas pipe assembly generally further includes a pre-silencer disposed intermediately thereof and a main silencer disposed at a rear portion thereof for reduction of exhaust noise. Because each of the pre-silencer and the main silencer is a chamber having a sufficient volume, these chambers are offset transversely of the vehicle body with respect to an extended line of a longitudinal axis of an engine output shaft i.e., a center line of the vehicle body for prevention of interference between these chambers and a propeller shaft or the like (Japanese Utility Model Laid-open Application (unexamined) No. 2-64712). Accordingly, at least that portion of the exhaust gas pipe assembly which extends rearwardly from an intermediate portion thereof is offset transversely with respect to the center line of the vehicle body.
The generally longitudinally extending exhaust gas pipe assembly is secured at a plurality of locations to the vehicle body (including a power plant system) via support members. Each of the support members includes an elastic member (vibration insulator) made of an elastic material, for example rubber, for absorbing relative displacement or vibration between the exhaust gas pipe assembly and the vehicle body. Each of the support members generally further includes an upper hanger having one end secured to the vehicle body and the other end connected with an upper portion of the elastic member and a lower hanger having one end secured to the exhaust gas pipe assembly and the other end connected with a lower portion of the elastic member.
In such support members, the allowance of displacement of the elastic members, in which displacement may occur, differs according to the direction, as viewed from above. For example, when a long and slender hanger extends through and is connected with an elastic member, the deformation of the elastic member is restrained by the hanger in the direction in which the hanger extends. Accordingly, the allowance of displacement becomes small in this direction. On the other hand, because the deformation of the elastic member is not restrained so much in a direction perpendicular to this direction, the allowance of displacement becomes large. Any support members can effectively absorb relative displacement or vibration between exhaust pipes and the vehicle body in the direction in which the allowance of displacement of the elastic member is large, but they cannot absorb it so much in the direction in which the allowance of displacement is small.
In an automotive vehicle equipped with an internal combustion engine disposed longitudinally thereof, the "rolling" of the engine and a transmission causes displacement or vibration of exhaust gas pipes in a direction transversely of the vehicle body. When an exhaust gas pipe assembly is offset or disposed away from the center line of the vehicle body, as mentioned previously, the transverse displacement or vibration thereof caused by the "rolling" is enlarged. On the other hand, the inertia force produced at the time of acceleration or deceleration or thermal expansion of the exhaust gas pipe assembly causes displacement or vibration in a direction longitudinally of the vehicle body. Accordingly, the exhaust gas pipe assembly is subjected to displacement or vibration at least in the directions longitudinally and transversely of the vehicle body. However, because the aforementioned support members cannot effectively absorb displacement or vibration of the exhaust gas pipe assembly in both the directions, the exhaust gas pipes are subjected to large stresses, which lower the durability thereof.
In an automotive engine such as, for example, a V-type engine having two banks i.e., two rows of cylinders, the banks have respective exhaust gas passages, which join a single exhaust gas manifold disposed downstream thereof (Japanese Utility Model Laid-open Application (unexamined) No. 62-67921).
In an automotive vehicle equipped with a V-type engine disposed longitudinally thereof, two exhaust gas passages generally extend longitudinally thereof on both sides of the engine and a transmission. The two exhaust gas passages join a single exhaust gas manifold disposed rearwardly of the transmission. The exhaust gas manifold generally extends longitudinally of the vehicle body, and therefore, an exhaust gas pipe assembly comprising the two exhaust gas passages and the exhaust gas manifold generally takes the form of a figure "Y".
In the exhaust gas pipe assembly in the form of the figure "Y" is generally employed an triple pipe or Y-shaped pipe integrally formed, for example, by casting. Accordingly, the Y-shaped pipe constitutes part of the two exhaust gas passages and part of the exhaust gas manifold. In other words, each of the exhaust gas passages includes a front portion of the Y-shaped pipe whereas the exhaust gas manifold includes a rear portion of the Y-shaped pipe. The Y-shaped pipe is connected with adjoining pipes by means of flanges.
The exhaust gas pipe assembly is connected at its front portion with two exhaust gas manifolds disposed on both sides of the engine and communicating with combustion chambers defined in respective cylinders. The exhaust gas pipe assembly is further connected to only at least one of the exhaust gas passages with a transmission casing via a support member and at the exhaust gas manifold with the vehicle body via another support member. To enhance the durability of the exhaust gas pipe assembly, the support members must be connected to those portions of the exhaust gas pipe assembly which have high rigidities. To this end, the support members are generally connected with flanges or any other suitable members having relatively high rigidities (Japanese Utility Model Application (examined) No. 1-43462).
When the exhaust gas pipe assembly including a plurality of elements is mounted on the vehicle body, front ends of two exhaust gas pipes constituting respective exhaust gas passages are initially connected with rear ends of the corresponding exhaust gas manifolds. Rear ends of the two exhaust gas pipes are then connected with the corresponding front ends of the Y-shaped pipe. During assembling, there generally arise slight variations in the positions at which the elements are connected i.e., these positions are not always fixed. However, because the configuration of the Y-shaped pipe to be connected with the two exhaust gas pipes cannot be changed, it is difficult for the Y-shaped pipe to absorb such variations. As a result, there arises the problem in that the accuracy in assembling the Y-shaped pipe would be lowered.